The present invention is directed to a corona discharging device for use with an image forming apparatus such as a copying machine or the like.
The image forming apparatus, such as a copying machine incorporates the corona discharging device for electrifying a photosensitive body. For the purpose of stabilizing an electrifying potential on the photosensitive body, there is provided a corona discharging device known as a so-called scorotron type in which a mesh-like grid plate, defined as a control grid is interposed between the photosensitive body and a corona wire. The grid plate is typically mounted on the corona discharging device and is so constructed as to be attachable to and detachable from the copying machine body together with the corona discharging device.
A long stretch of use of the corona discharging device, however, causes the adhesion of foreign matters to the corona wire or contamination of an interior of a shield case, which in turn requires periodic cleaning. On that occasion, an easier workload necessitates removal of the grid plate attached to the corona discharging device. The removed grid plate has to be, as a matter of course, remounted on the corona discharging device.
In order to facilitate the attachment and detachment of the grid plate with respect to the corona discharging device, a variety of proposals have hitherto been made. For instance, as disclosed in (1) Japanese Laid-Open Utility Model Publication No. 143961/1987, end blocks for holding the corona wire are fixedly provided at both ends of the corona discharging device, engaging members integrally standing erect on the end blocks. One of the engaging members is arranged to be elastically deformable, whereby the engaging members engage with slits conceived as engaged parts of the grid plate.
As is also disclosed in (2) Japanese Laid-Open Utility Model Publication No. 30268/1987, an engagement portion formed on a U-shaped spring member detachably mounted on a discharging body engages with one of the slits formed in the grid plate.
The first of the prior art corona discharging devices, however, presents the following problems. The grid plate is stretched with a tension by an elasticity of one of the engaging members, and hence a distance between the engaging members disposed at both ends of the corona discharging device in the longitudinal direction has to be longer than between the slits formed on both ends of the grid plate. As a result, when fitting the grid plate to the thus constructed corona discharging device, the engagement portion shaped by an elastic protrusion has to be deformed beforehand, or, alternatively, the grid plate is required to be pulled inwards to the greatest possible degree. The attachement thereof is therefore quite troublesome. Besides, dismounting the grid plate involves operations reversed to the above, so that the troublesome situation is the same.
The second of the prior art corona discharging devices is attended with the following problems. It is difficult to insert the U-shaped spring member into the discharging body, resisting the resilient force thereof. Even if inserted, the spring member will probably spring out of the discharging body due to its resilient force. In addition, the configuration of the corona discharging device becomes intricate, and its assembly is also troublesome.